The present invention relates to a zoom lens, particularly a zoom lens intended for use with 35 mm SLR cameras, the focal length of which is approximate 400 mm at a telephoto end, which has a zoom ratio of two or more, substantially the same brightness as a fixed focus lens, and substantially the same performance and compactness as a fixed focus lens.
To date, there have not been many zoom lenses available having telephoto end focal lengths of approximately 400 mm for use with 35 mm cameras. The primary reason for this is that while a lens having a focal length of 400 mm requires a relatively large aperture ratio, compactness is also required so that the lens may be manually operated without photographic support means such as a tripod.
In general, in a lens of this type, if the overall length is decreased, the chromatic aberration (secondary spectrum) is increased and at the same time, due to the decrease of the Petzval's sum, curvature of field and astigmatism are increased resulting in a deterioration in performance. In case of super-telephoto lenses have a focal length of 800 or 1000 mm, the F-number of the lens is generally large. That is, the lenses pass sufficiently small quantities of light such that the image curvature distortion and astigmatism can be covered by the depth of focus to thereby facilitate miniaturization. However, since a relatively large aperture ratio is required for 400 mm lenses, it is difficult to miniaturize the lenses. This tendency is more remarkable in zoom lenses in which a telephoto end focal length is approximately 400 mm. It is very difficult to construct a zoom lens having a large aperture ratio and which is compact and exhibits good performance over the entire zoom range.